It seems pretty simple. If Google is interested in improving what many consider the massive problem of fake reviews posted on Google Plus for Business listings (Google Places and Maps) they could separate reviewers by verified and non-verified reviewers.
To verify a reviewer they could use the same process or a similar process to how a business is verified on Google Places. Just send then a code to their cell phone, or send them a letter with that code to their postal address.
Imagine the improvement in quality of reviews! Google could then at least list the city a reviewer is in for the public, and the “reviewer” would then have at least some sense of accountability. In the very near future it is highly likely you will be hearing about businesses suing other businesses over fake reviews (negative in nature) and Google being forced to release IP and other information on a reviewer.
If Google is truly concerned with the value of these reviews, they could implement this in a week. What are your thoughts?